This invention relates to a method and apparatus for washing a sliced silicon ingot, and more particularly to a method for washing a silicon ingot which has already been sliced to form a plurality of silicon wafers.
As is well known in the prior art, a silicon wafer is formed by cutting or slicing a certain thickness such as, for example 880 .mu.m from a silicon ingot having a generally cylindrical shape. In this instance, the silicon ingot is supported by a holder of a cutting machine. Slicing the ingot generates a substantial amount of particulate matter which adheres to the ingot. After the silicon ingot has been sliced, it is immersed in a bath containing a relatively costly detergent. The detergent includes a surfactant and a special oil to remove the particulate matter. The detergent is preferably used to as long as possible because of its substantial cost.
However, the detergent rapidly becomes filled with the particulate matter which results in a loss of chemical activity of the detergent. It will then no longer effectively remove the particulate matter from the ingot and must be replaced with fresh detergent.
In light of the above, it is a principal object of the present invention to provide an improved method and apparatus for washing a sliced silicon ingot for substantially slowing the rate of loss of chemical activity of the detergent.
Another object of the invention is to provide an improved method and apparatus for washing a worked silicon ingot for reducing the consumption of detergent.
Generally, a method for preparing semiconductor wafers from monocrystalline ingots comprises the steps of mounting the ingot on a holder. The ingot is sliced through at closely spaced longitudinal intervals thereby forming slits, each pair of slits defining a semiconductor wafer in the ingot. The sliced ingot is washed with water to remove particulate matter from the ingot which was generated during the step of slicing through the ingot and adhered to the ingot and which accumulates in the slits. Washing the ingot with detergent chemically removes particulate matter remaining following the step of washing the ingot with water. The step of washing the ingot with detergent occurs after said step of washing the ingot with water. The wafers are then separated from the holder for further individual processing of the wafers.
In another aspect of the invention, a apparatus for pre-washing a sliced silicon ingot generally comprises a support for holding the ingot. Nozzles are adapted to deliver jets of water against the ingot for flushing particulate matter from the ingot. A carrying device mounts the nozzles for movement longitudinally back and forth over substantially the full length of the ingot.